The present disclosure relates to a bearing member which supports a driven roller, a sheet conveying device which conveys a sheet along a conveying path and an image forming apparatus provided with this sheet conveying device.
In an image forming apparatus, a sheet fed from a sheet feeding cartridge to a conveying path or a sheet fed to an inversion path for duplex printing is conveyed to a downstream side of the conveying path by a sheet conveying device. Such a sheet conveying device is generally provided with a driving roller rotationally driving and a driven roller which comes into pressure contact with an outer circumferential face of the driving roller, and is configured to convey the sheet between the driving roller and the driven roller.
In the conveying device of such a configuration, the driven roller is supported so as to come into pressure contact with the driving roller at a predetermined pressure. In order to support the driven roller so as to come into pressure contact with the driving roller, there may be a case in which a rotating shaft of the driven roller is made of metal and the rotating shaft is biased toward the driving roller by an elastic member such as a coil spring. On the other hand, in a sheet conveying device of an image forming apparatus of a low speed specification, there may be a case in which a rotating shaft of a driven roller is made of resin, and this rotating shaft is biased toward the driving roller by an elastic member such as a linear spring.
In addition, a bearing member using a torsion coil spring as an elastic member may be sometimes used. In this bearing member, one end part of the torsion coil spring is tightly wound in a spiral shape to form a winding part into which the rotating shaft of the driven roller is rotatably supported and, therefore, the driven roller comes into pressure contact with the driving roller by a biasing force of the torsion coil spring.
However, in the case of the rotating shaft made of metal, there is a problem that abnormal noise is easy to be generated. As a solution to this problem, there may be a case in which a countermeasure to apply a grease to the surface of the rotating shaft or to apply a high sliding coating on the surface of the rotating shaft may be taken. Alternatively, there may be a case in which the rotating shaft is formed with a plane portion for functioning as a rotation stop of the rotating shaft. Although a variety of countermeasures have been thus taken, in any case, higher costs are unavoidable.
Also, in the case of the rotating shaft made of resin, although there is no problem in the image forming apparatus of a low speed specification, when applied to an image forming apparatus of a high speed specification, since abrasion of the rotating shaft due to contact with a pressing member is severe, the rotating shaft is deteriorated in durability.
In addition, in the case of the bearing member using the torsion coil spring, at attaching the bearing member, since it is necessary to position the bearing member at two positions, that is, at the coil part of the torsion coil spring and at an opposite end part to the winding part, there is a problem that attachment work of the bearing member is complicated.